Rolling mills



Aug. 20, 1963 H. GILL ROLLING MILLS Filed Feb. '25. 1960 Y. E N Wm 2 o T5 M Elv Me U M m H United States Patent 3,1tll,016 ROLLING MILLs :HedleyGill, Shetfield, England, assignor to The British This invention relatesto rolling mills and is particularly concerned with the control of amulti-stand rolling mill. While the invention has chief application tothe cold roll- 3,101,016 Patented Aug. 20, l 953 and hence a change inspeed of the strip leaving the first stand and entering the secondstand. This in turn alters the reduction efiected at the second andsubsequent stands of the mill, so that the strip leaving the millas awhole may not have the desired thickness. It is therefore necessary,either to adjust one or more of the other stands of the mill or tosupply automatic gauge control on at least the last stand of the mill,as Well as the-first stand. Duplication of the automatic control systemis expensive.

To ensure that adjustment of screwdown on the first stand of the milldoes not affect the rolling performance ing of strip, it may be appliedto the rolling of hot strip, 7

provided that there is substantial interstand tension.

In the cold rolling of steel strips in a multi-stand mill, the incomingstrip is liable to vary in thickness along its length and it isdesirable to provide .means for adjusting at least one of the stands tovary the reduction. This adjustment is usually effected by adjustmentof'the screws on the first stand. However, the adjustment on the firststand alters the rolling conditions on subsequent stands and hence thereductions produced by the succeeding stands. An object of thisinvention is to provide a means for preventing the adjustment of theroll setting on any stand, but more particularly the first stand, fromaffecting the operation of subsequent stands. v

Inaccordance with the present invention, a multistand rolling mill hason one of the stands preceding the last stand in the train a controlsystem for controlling to a desired value the speed of the strip leavingthe stand, irrespective of adjustments to the roll setting of thatstand. The roll setting of the selected stand can then be adjusted,during rolling, for example in order to compensate for variations inthickness of the incoming strip, without affecting the operation ofsucceeding stands.

Preferably, the stand provided with automatic strip speed control has agauge control system for automatically maintaining substantiallyconstant the thickness of the strip leaving the stand.

The invention will be more readily understood by way of example from thefollowing description of control systems for a multi-stand tandem mill,reference being made to the accompanying drawings, in which FIGURE 1diagrammatically illustrates the mill,

FIGURE 2 schematically shows the control system for one of the stands,preferably the first stand in the train, and

FIGURE 3 illustrates a tensiometer for the strip.

Referring to FIGURE 1, the mill consists of a number of stands, of whichonly the first two and the last stand is illustrated. Each stand isrepresented by a pair of work rolls 12, 13; 12a, 13a; 12b, 131), a drivemotor 14, 14a, 1 21] and a screwdown motor and control gear therefor 15,15a, 15b. The screwdown motor 15, when operated, adjusts the rollsetting, i.e. the nominal separation of the rolls. It will beappreciated that, Where desired, each of the rolls i2, 13 may be drivenby a separate motor In.

The various stands are set up so that each reduces the stripappropriately to produce a desired overall reduction in the mill. Forthis purpose, the interstand tensions are carefully selected, since thereduction effected at any one stand depends, not only on the rollsetting of that stand, but also on the tensions in the strip at eachside of the stand. In order to produce strip of reasonably constantgaugc, at least one of the stands must be controlled during rollingeither by hand or automatically. This adjustment is usually etfected bycontrolling the roll setting on the first stand, for example toeradicate changes in thickn ss in the strip entering the mill. However,change in the screwdown on the first mill results in an alteration inthe reduction of the strip in that stand of subsequent stands, the motor14 of that stand, or motors 14 where each of the rolls 12, 13' is drivenindependently, is automatically controlled so that the speed of thestrip leaving the first stand is maintained substantially constant. As aresult, the interstand tensions remain constant, irrespective ofadjustments efiected at the first stand, and the reductions effected atsucceeding stands remain unaltered.

FIGURE 2 illustrates one way in which the speed of the strip leaving therolls 1-2, 13 may be maintained constant. A tacho-generator 16 is drivenby a roller 17 in contact with and driven by the strip 18 at the exitside of the rolls 12, 13. Roller 17 may be the roller of a tensiometer,as illustrated in FIGURE 3. The DC. signal from the generator 16, whichis proportional to the strip speed, is applied in opposition to thevoltage from potentiometer 26 to the input of a high-gain amplifier 21.Potentiometer 26 is adjustable by hand to a value representing thedesired strip speed, so that the input signal to amplifier 21 isdependent on the divergence of the strip speed from the desired value.Amplifier .21 feeds the field winding 22 of a generator 23, the armatureof which is connected to the armature of the motor 14 driving the rolls12, 13. If the speed of the strip 18 changes, due for example toalteration of the screwdown of the rolls 12, 13, the armature voltage ofmotor 1 is altered to change the speed of rolls 12, 13 until the stripspeed is returned substantially to the value set by the potentiometer20. 1

During rolling, the screwdown of rolls 12, 13 is automatically adjustedto maintain substantially constant the thickness of the strip leavingthe stand. This adjustment may be effected by hand'but is preferablyeitected by an automatic control system such as that described in US.Patent 2,726,54l to R. B. Sims, and illustrated for convenience inFIGURE 2. Sims describes a circuit for generating an electric signalrepresenting the departure of the strip thickness (71) from the desiredstrip thickness (h) and this error signal is shown in FIGURE 2 asapplied to the motor and control circuit 15 to cause the screwdown to beadjusted to maintain the error substantially zero. While referenceshould be made to Sims for a more detailed description of the circuit,that circuit will now be briefly described for convenience.

A slider 24 on a resistor R1 is coupled to the screws of the rolls 12,13 so that the voltage developed between the slider 24 and a secondslider 25 on resistor R1 is proportional to the roll setting (S of therolls 12, 13, resistor R1 being energised by a battery B1. A Wheatstonebridge network 25 is constituted by four resistance strain gaugessupported on a block between the checks for the roll 12 and the screw.The bridge 26 is energised by a battery B3 and the voltage from thebridge is proportional to the separating force (F) generated in thestand. A second resistor R2, energised by battery B2, has a contact 27which can be adjusted by hand in accordance with the desired thicknessof the strip (11'). The contacts 24, 25, 27 and the bridge 26 areconnected in series so that the voltage developed across lines 28, 29 isequal to F/M+S -h', where M is the spring factor of the stand,

or to the departure of the strip thickness from the desired vvalue, vh.This signal is applied to an amplifier 30, the

output of which controls the control circuits for the screwdown motor15.

The speed of the strip 18 leaving the rolls 12, 13 is, of course,related to the tension in the strip 18 between the rolls 12, 13 and therolls 12a, 13a. If the speed is kept constant then the tension will beheld within narrow limits, and vice versa. In the modification of FIGURE3 the tacho-generator 16 of FIGURE 2 is replaced by a conventional striptensiometer, represented by a jockey pulley 34 biased upwardly againstthe strip 18 by a spring 35and coupled .to the sliding contact 36 of apotentiometer 37. The voltage on sliding contact as is then dependent onthe interstand tension and is applied in opposition to the voltage frompotentiometer 20 (FIGURE 2) to control the armature voltage of motor 14,as before, in order to maintain the tension substantially constant.

In another modification, the signal from amplifier 21, when thatamplifier is controlled by strip speed or tension, is employed tocontrol the speed-torque characteristic of motor 14. The armaturevoltage is kept constant but the inclination of the speed-torque line Vis varied to adjust the speed of the motor for constant torque.

It has already been explained that the change in the roll setting of therolls 12, 13 causes an alteration of the strip speed, due to the changedreduction etfccted by the rolls 12, 13. Simultaneously, the change inroll setting causes a change in strip speed in the opposite direction,due to the speed-torque characteristic of the motor 14 and thealteration in the torque required of the motor as a result ofthe changedreduction. In a further modification, these facts are used to maintainthe strip speed constant, without a closed-loop control system such asthat illustrated by the tacho-generator 16, amplifier 21 and generator23. Thismay be done by appropriately varying in known manner theinclination of the speed-torque characteristic of the motor 14 so thatthe change in strip speed resulting from the required change in torqueis equal and opposite to the change in strip speed resulting from thechange in reduction.

' In the systems illustrated in FIGURE 2 and FIGURE 3, means (not shown)are supplied for protecting the control system against failure of thedetectors 1 6, 34. In the event of failure of the detector the speed ofmotor 14 is automatically prevented from rising beyond a safe value.

between and in contact therewith, driving means connected to each pairof said rolls for driving each of said rolls in opposite directions fromone another, a gauge control system controlling the roll sett ing of atleast one stand preceding a last stand of said plurality of stands tomaintain the thickness of a strip of material leaving said one stand atsubstantially a constant value, a speed 5 control system connected tosaid driving means for controlling the speed of the rolls of said onestand and responsive to the speed of the strip of material leaving saidone stand for maintaining a constant speed of the material leaving saidone stand.

2. A rolling mill as set forth in claim 1 wherein said driving means isresponsive to electrical signals and said speed control system generatesan electrical signal depending on the speed of the strip of materialleaving said one stand to energize said driving means to control thespeed of the strip of material leaving said one stand.

5 References Cited in the file of this patent V UNITED STATES PATENTSOTHER REFERENCES Bringing Hot Strip Mills Under Automatic Control,

ControlEngineering, September 1960 (pages 146149). (Copy in 80-56E.) I

Continuous Gaging Automation, March 1956 '(pages 52-57). 7 (Copies in8056E.) I

1. A MULTI-STAND ROLLING MILL COMPRISING A PLURALITY OF STANDS, EACHSTAND HAVING A PAIR OF OPPOSING ROLLS ARRANGED TO RECEIVE A STRIP OFMATERIAL AT THE NIP THEREBETWEEN AND IN CONTACT THEREWITH, DRIVING MEANSCONNECTED TO EACH PAIR OF SAID ROLLS FOR DRIVING EACH OF SAID ROLLS INOPPOSITE DIRECTIONS FROM ONE ANOTHER, A GAUGE CONTROL SYSTEM CONTROLLINGTHE ROLL SETTING OF AT LEAST ONE STAND PRECEDING A LAST STAND OF SAIDPLURALITY OF STANDS TO MAINTAIN THE THICKNESS OF A STRIP OF MATERIALLEAVING SAID ONE STAND AT SUBSTANTIALLY A CONSTANT VALUE, A SPEEDCONTROL SYSTEM CONNECTED TO SAID DRIVING MEANS FOR CONTROLLING THE SPEEDOF THE ROLLS OF SAID ONE STAND AND RESPONSIVE TO THE SPEED OF THE STRIPOF MATERIAL LEAVING SAID ONE STAND FOR MAINTAINING A CONSTANT SPEED OFTHE MATERIAL LEAVING SAID ONE STAND.